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SKIP HOIST CONTROL I Gordon Fox, Chicago. Ill., assigner to Freyn ngineering Company, Chicago, lll., a corporation of Maine Application December 29, 1944, Serial No. 570,310

19 Claims. l

The present invention relates to improvements in skip hoist controls.

More particularly the present invention relates to improvements in mechanism for controlling the motors of a skip hoist such as used in the charglng of a blast furnace. According to preferred practice, skip hoists for blast furnaces involve two skips, one being used to haul material to the top of the furnace while the other is descending to the skip pit. It is preferred practice to provide the hoist with a drive having two motors. The mechanical features of a two-motor drive for a skip hoist are described and claimed in the application of Fox, Callow and Bigelow, filed February 23, 1942, Serial No. 432,060, now Patent No. 2,345,662, dated April 4, 1944.

In the application filed by the present applicant 'on December 1i, 1942, serial No. 468,698, now

Patent No. 2,379,958. dated July 10, 1945, it was pointed out that a dominating factor determining the size of the hoist motors is the torque required in starting and accelerating. The torque demanded during this period, at the time when one of the skips is at the furnace top (therefore not providing counterbalance), is about twice as great as the torque required under full speed running conditions. In the Fox application Serial No. 468,698 referred to, a drive was described using series-parallel control for the lower portion of the speed range and shunt field control of the hoist motors for the upper portion of the speed range. This combination affords basically a very large torque production per ampere at low speeds and diminishing torque capacity at high speeds. It

permits the use of higher gear ratios, and it employs motor capacity more effectively than conventional drives having the same torque capacity at all speeds.

The application filed by the present applicant on May 19, 1943, Serial No. 487,550, now Patent No. 2,370,855, dated March 6, 1945, describes and claims an improvement in skip holst controls involving variable (adjustable) voltage control. In the driving mechanism described and claimed in said application, variable (adjustable) voltage is employed for the lower portion of the speed range only, and shunt field control of the hoist motors is employed for the upper portion of the speed range. According to the disclosure of that application, a generator is employed feeding two hoist motors whose armatures are connected in series (or in parallel). The generator field windings are supplied from an exciter. Provision is made to vary the strength of the generator field in order to vary the voltage. Two brakes are provided 2 whose operating coils are connected in series across the exciter. The two shunt fields of the two hoist motors are similarly connected in series and are supplied from the exciter. and resistors and relays are provided to vary their strength.

According to the Fox application Serial No. 487,550, referred to, the generator field is not reversed and the generator voltage is consequently unidirectional. The direction of rotation of the hoist motors is changed by armature-reverslng contactors (which are opened and closed only under zero voltage and zero current conditions). This arrangement is employed because themotors are equipped with stabilizing windings. The current must always flow through these windings in the same direction. These windings are essential to the stable operation of the motors with weakened fields. The gear ratio between the motors and the hoist drum is substantially greater than in prior conventional practice. In view cf this fact, and also because field-forcing is used at low speeds, motors of a given frame develop more torque at the hoist drum per armature ampere. The more effective use of the motors is reflected in more advantageous employment of the generator capacity.

The present invention relates to variable voltage control and provides a novel arrangement involving a three-unit motor generator set which may be located in the hoist house of each blast furnace. The motor generator sets at a plurality of blast furnaces at a single plant may be connected together for cooperation in a manner which will be described presently. According to an installation which has been placed in service, a three-unit motor generator set comprises a 600 horse power synchronous motor driving two approximately duplicate generators. One of these generators is rated at 250 kilowatts, 300 volts. This generator supplies adjustable voltage for the two motors driving the skip hoist. The other generator is rated at 200 kiiowatts, 240 volts. This generator supplies the constant potential direct current service to the scale cars, cranes. and other auxiliary drives about the furnace.

An object of the present invention is to provide a novel skip hoist control involving a motor generator set comprising one driving motor and two approximately duplicate direct current generators for a suppy of adjustable voltage for hoist operations and a supply of constant potential for general service, including provisions whereby either generator can be used to supply adjustable voltage for hoist service.

A further object is to provide a skip hoist control oi the kind immediately above referred, to in which either. generator or both generators cansupply constant potential for general service.

A furtner obJect is to provide a novel control for a skip hoist in .which one direct current generator may be employedas a motor operating from a constant potential source (either from an adjacent skip hoist installation or from an i outside source) to drive the other direct current ,blast furnaces may operate to supplement each other.

A further object is to provide an improved skip hoist control employing hoist driving means and a motor generator set including two generators, together with control mechanism whereby one of said generators may be employed to supply adjustable voltage to the hoist driving means and the other generator may be employed to supply constant voltage requirements of the hoist driving means, a further provision being made that the second named generator may be employed alternatively to supply adjustable voltage to the hoist driving means and the constant potential requirements of the hoist may be supplied from a separate source.

A further object is to provide an improved skip hoist control well adapted to meet the needs oi commercial service.

Further objects will appear as the description proceeds.

Referring to the drawings- Figure 1 is a diagrammatic layout illustrating the principles of the present invention as applied to a plurality of skip hoists at a like number of blast furnaces.

Figure 2 is an electrical diagram showing the electrical connections of a preferred embodiment of the present invention, said Figure 2 being divided into three parts, as follows: Figure 2-part A; Figure 2-part B; Figure 2-part C.

Figure 2, part A-l; VFigure 2, part B-l; Figure 2,part C-l, are explanatory diagrams for simplifyinar the matter of locating, identifying and correlating the various elements, such as coils and contacts, of the various instrumentalities appearing in the corresponding parts of Figure 2.

* Figure 3 is a development of a drum controller or its equivalent, a cam limit switch, forming part of theembodiment of the invention illustrated in the preceding gures.

Figure 4 is a simplified diagram of Figure 2, certain instrumentalities being omitted from Figure 4 for purposes of simplicity.

Figure 5 is a top plan view of a hoist provided with two driving motors and two brakes.

Figure 6 is a more or less diagrammatic view illustrating part of a blast furnace, a skip incline associated therewith, a pair of skips, and an end elevation of the hoist for operating said skips.

Figure 7 is a side elevation of a hoist on approximately the same scale as the hoist shown in Figure 6.

Relerring first to Figures 5, 6 and 7, Figure 5 illustrates a pair of driving motors MI and M2.

Said motors are connected, respectively, to brakes indicated as Brake I and Brake 2 by means of couplings 3 and 4. Said brakes Brake I and Brake 2 are connected, respectively. to gear reduction units 'I and 8. The low speed sides of said Sear reduction units 'I and 8 are connected, respectively, to pinions 8 and I0 which mesh with the gear I I. Said gear I I is rigidly secured to the drum I2, which has secured thereto the cables I3 and Il. Said cables I2 and I4 may be connected, respectively, to the right skip and the left skip oi' a blast furnace charging mechanism. It will be understood that when one or both of the motors MI-M2 are energized to cause rotation of the winding drum I2 in one direction, one of the cables will be wound up upon the drum I2 and the other of said cables will be paid oi, and, conversely, when the energization of one or both of the motors MI-M2 is such as to cause reverse rotation of the winding drum I2, the movements of said cables I3 and I4 will be reversed. Limit switch means connected to be driven in synchronism with the drum I2 are indicated diagrammatically by the numeral I5.

Referring to Figure 6, the numeral IG indicates a blast furnace and the numeral il indicates a skip incline associated with said blast furnace. Said skip incline is provided with a pair of skips I8 and I9, one of which is illustrated as being in the skip pit 20 and the other of which is indicated in capsized position for delivering material into the hopper 2| at the top of the blast furnace I6. The skip I8 is shown in position to receive material from the scale car 22. The cables |'3 and I4 associated with the winding drum I2 are connected to the two skips I9 and I8, being trained over sheaves which need not be described in detail.

Referring now to Figure 1, a diagrammatic layout is illustrated showing the connections at a plurality of blast furnaces. Two blast furnaces are illustrated, but the installations at any number of blast furnaces may be connected up in the manner illustrated in Figure 1. The layout at each blast furnace may be like that at each of the other blast furnaces, and a description of one will suffice for all. Figure 1 for purposes of simplicity shows two or three wire circuits as a single wire. Two generators GI and G2 are illustrated, which with the motor M3 form a motor generator set. Said motor M3 is illustrated as being disposed between the generator GI and G2, the shafts of said generators and said motor being in alignment. The shaft of the motor M3 is connected to the shaft of the generator GI by a coupling Coup. i', and said shaft of the motor M3 is connected to the shaft of the generator G2 -by means of a coupling Coup. 2. As will be explained presently, when it is necessary to remove the motor M3 from the assembly for repairs or for other reasons. said motor may be replaced by a dummy shaft temporarily coupled to the couplings Coun. I and Coup. 2. Said motor M3 is adapted to be connected to a source nf A. C. sunnlv through the three-pole switch KS2I.

Hoist motor busses (indicated by a single line) bear the characters Hill/133+ and HMB-. Constant potential busses indicated bv a single line bear the characters CPB-|- and CPB-. Switches KS2, KS? and circuit breakers indicated as accuse BKRI, BKR2 and BKR: are provided -havlng functions ofcontrolling the circuits between said hoist motor busses and said constant potential busses, and a control assembly which comprises un assembly of contactors, relays, and other secondary elements of the control for the hoist, all of which are shown more in detail in other figures and will be described presently. Said Figure 1 also illustrates in connection with each of the blast furnace installations a starter which is an assembly of contactors, relays, resistors and associated parts necessary to starting the unit Gl as a motor. The details as used in each of the blast furnace installations is shown more in detail in the upper portion of Figure 2-part A, above the switch KS2.

The installations at the various blast furnaces are connected together by means of a tie circuit indicated as Tie circ., which tie circuit may also be connected to an independent source of direct current supply such as a substation. The tie circuit is connected to the several constant potential busses CPB+, CPB-, by means of circuit breakers indicated by the character BKRI.

Figure 1 also indicates feeder circuits adapted to be supplied from the constant potential busses CPB+, CPB, for the supply of current to operate scale cars, cranes, and other auxiliary drives about the furnace. Certain instrumentalities associated with the motive means of the hoist also require constant potential. These instrumentalities are the following, to be referred to with more particularity hereinafter.

Synchronous motor field (Syn. mtr. fld.) of the driving motor M3.

Field windings (Gen. fld. I and Gen. fld. 2) of the generators G-I and G-2, respectively.

The shunt field windings (Mtr. sh. fld. l' and Mtr. sh. fld. 2) of the motors Ml and M2, respectively.

The coils (Brake l and Brake 2) of Brakes l and 2, respectively.

The control circuits of the various contactors and relays.

A detailed explanation of the electrical instrumentalities involved in the illustrated embodiment of the present invention may be prefaced by a statement of the significance of the numerals and letters used thereon, as follows:

The letters AT refer to the operating coils and contacts responsive thereto of various timing relays of a magnetic motor starter.

The letter A refers to the operating coils and contacts responsive thereto of accelerating relays of a magnetic motor starter.

The letters GM refer to the operating coil and contacts responsive thereto of the main starting cont-actor of a magnetic motor starter.

The letters R, as for example RI-R2, Ril-R9, refer to resistors in the magnetic motor starter circuit and the generator field circuits.

The letters MR refer to the resistors in the motor shunt field circuit.

The letters GF refer to the operating coils and contacts responsive thereto to the generator field relays.

The numerals H and I3 following the letters LU. and the numerals l2 and I4 following the letters RU` as for example RU|`2 and LUI3. refer to instrumentalities particularly associated with motor No. I.

The numerals 2| and 23 following the letters LU. and the numerals 22 and 24 following the letters RU, as for example RU22 and LU23, refer to instrumentalities particularly associated with motor No. 2.

The letters LU refer to the operating coils and contacts responsive thereto of contactors which function only to cause the left skip to travel up the incline.

The letters RU refer to the operating coils and contacts responsive thereto of contactors which function only to cause the right skip to travel up the incline.

The letters FW refer to the operating coils and contacts responsive thereto of motor field weakening relays which function to accelerate the hoist motors and to decelerate them.

The letters BR refer to the operating coil and contacts responsive thereto of the brake relay.

The letters UV refer to the operating coil and contacts responsive thereto of an under-voltage or low-voltage relay.

The letters LSU refer to the operating coil and the contacts responsive thereto of a relay controlling the movement of the left skip up.

The letters RSU refer to the operating coil and the contacts responsive thereto of a relay controlling the movement of the right skip up.

The letters LS refer to the contacts of the limit switch elements controlling upward movement of the left skip.

The letters RS refer to the contacts of the limit switch elements controlling upward movement of the right skip.

The letters LSUB refer to a push-button control for starting the left skip up.

The letters RSUB refer to a push-button control for starting the right skip up.

The letters FT refer to the operating coil and contacts responsive thereto of a timing relay associated with one of the field weakening relays.

The letters CBR refer to the operating coil and contacts responsive thereto of the series brake relay.

The letter T refers to the operating coils and contacts responsive thereto of various timing relays.

The letters SDR refer to the operating coils and contacts responsive thereto of slow-down relays, ISDR referring to first slow-down and 2SDR referring to second slow-down.

In general, contactors and relays are identified by the characters applied to their operating coilsand the contacts are differentiated b v the addition of suffixes. For example, the character 3A represents the operating coil of a corresponding contacter. and character 3Aa represents the contacts of this contacter.

Referring now to Figure 2, which is in three parts, to wit-part A, part B and part C, the various circuits are shown in greater detail. The three-pole switch KS2! (Fig. 2, part A) is shown as controlling the three terminals of a source of three-phase A. C. supply to connect said source to the synchronous motor M3. Double-pole knife switches KS2 and KST and circuit breakers BKRI and BKRZ are provided for connecting either or both generators Gi and G2 to the D. C. constant potential busses indicated by the letters CPB-L. CPB-, or for connecting either generator to the hoist motor busses indicated by the letters HMB+, HMB-. A D. C. bus circuit breaker BKR3 is provided which may be used for connecting the fields of the motor M3 and the field and brake control busses indicated by the letters FBCB-land FBCB-, to the constant potential busses CPB-i, CPB- A double-pole knife switch KBI (Fig. 2, part A) is provided for connecting motor starter control circuits to the constant potential busses CPB+ and CPB- when generator GI is to be operated as amotor. The starter.` indicated schematically in Figures 1 and 4, is, as stated above, an assembly o! contactors. relays. resistors and associated parts necessary to the starting oi' the unit GI as a motor. The details of the starter are illustrated in Figure 2, part A. above the double-pole, double-throw switch KS2. The single-pole, double-throw knife switch KSB connects this starter into the armature circuit of the unit GI In normal commercial operation according to the installation above mentioned the generator G2 will develop voltages varying from zero to approximately 325 volts D. C. maximum. Generator GI provides a constant potential D. C. supply of approximately 250 volts required for the brakes, the generator fields, the motor ields. and the coils of the magnetic contactors and relays.

The characters LI and L2 (Fig. 2, part A), represent the two sides of an electrical circuit across which are connected the magnetic contactors and relays for the starter when the unit GI is to be operated as a motor. Connected across the mains LI and L2 is a circuit including the coil of accelerating contactor coil 3A, timing relay contacts 3ATa biased to closed position and accelerating contactor contacts 2Aa biased to open position. Said contacts SATa are responsive to the timing relay coil 3AT, being held open when said coil IAT is energized. The contacts 2Aa are responsive to the accelerating contacter coil 2A. being held closed when said coil 2A is energized. Also connected across the mains LI, L2, is a. circuit including the accelerating contactor coil 2A, timing relay contacts 2ATa biased to closed position and accelerating contactor contacts IAa biased to open position. Said contacts 2ATa are responsive to the timing relay coil ZAT, being held open when said coil 2AT is energized. The contacts IAa are responsive to the accelerating contactor coil IA, being held closed when said coil IA is energized. Also connected across the mains LI and L2 is a circuit including the accelerating contactor coil IA, timing relay contacts IATb, biased to closed position, and main contactor contacts iGMc, biased to open position. Said contacts IA'Ib are responsive to the timing relay coll IAT, being held open when said coil IAT is energized. The contacts IGMc are responsive to the coil IGM of the main starting contactor, being held closed when said coil IGM is energized. Also connected across the mains LI, L2, is a circuit including the timing relay coil IAT and the main coil contacts IGMb, biased to closed position. Said contacts IGMb are responsive to the coil IGM of the main starting contactor, being held open when said coll IGM is energized. Also connected across the mains Li, L2, are the start button P and the stop button Q. When the start button P is depressed, its contacts are closed, and when the stop button Q is depressed, its contacts are opened. In the circuit of buttons P and Q are the coil of main starting contactar IGM and timing relay contacts IATa, biased to open position. In parallel relationship with the contacts IATa are the main coil contacts IGMa, biased to open position. The contacts IATa are responsive to timing relay coil IAT, being held closed when said coil IAT is energized. The contacts IGMa are responsive to coil IGM, being held closed when said coil IGM is energized.A Also connected across the mains LI. L2. is a circuit including the amature of the generator GI in series with a set or resistors having a number oi' taps designated as RI, R2. R3 and RI. Connected to the taps of these resistors are a plurality of relay coils and relay contacts. Across the taps RI-R2 are the relay contacts iAb: across the taps R2-R3 are the relay contacts 2Ab: across the taps RI-Rl are the relay contacts IAa. Also across the taps iti-R2 is the timing relay coil 2AT, and across the taps Ri-RI is the timing relay `coil IAT. The relay contacts IAb, 2Ab and IAa are all biased to open position and are adapted to be closed when their corresponding operating coils IA. 2A and 3A are energized. Also in series with the armature of the'generator GI are the contacts IGMd responsive to the main starting contactar coil IGM. Said contacts IGMd are biased to open position and are held closed when the corresponding operating coil IGM is energized.

Connected across the busses FBCB+ and FBCB- are the shunt fields of generators GI and G2 designated Gen. d. i and Gen. d. 2 (Fig. 2. part B). Double-pole knife switch KSN is provided to connect Gen. iid. l across the busses FBCB+ and FBCB- with the rheostat designated Gen. i iid. rheo. in circuit, or, alternatively. with resistors R5-R9 in circuit. Similarly, double-pole knife switch KSII is provided to connect Gen, iid. 2 across the busses FBCB+ and FBCB- with the rheostat designated as Gen. 2 ild. rheo. in circuit, or. alternatively, with resistors RFI-R9 in circuit. Connected to the taps of these resistors are a number oi' relay contacts. Across the taps RE-RS are the relay contacts GFIc; across the taps RG-RI are the relay contacts GFZa; and across the taps R'I-R8 are the relay contacts GF3d. The relay contacts GFIc,

40 GFZa and GF3d are all biased to open position and are adapted to be closed when their corresponding operating coils GFI, GF2 and GF3 are energized. Also in series with Gen. iid. 2 and the set of resistors are the generator lleld relay contacts GFb biased to open position and adapted to be held closed when their corresponding operating coil GF is energized.

Connected across the busses HMB+ and HMB- are the armatures of the motors MI and M2 in series with their respective series eld, Mtr. I ser. lid. and Mtr. 2 ser. d. Directional contactors RUI2b and RUIIb and RU22b and RU24b are provided for directing current in one direction through the armatures of the hoist motors MI and M2 respectively, and directional contactors LUI ib and LUI3b, and LU2Ib and LUZlb, are provided for alternatively directing current through said armatures in the opposite direction (Fig. 2, part A).

Connected across the busses FBCB+ and FBCB- (Fig. 2, part B) is a circuit including the resistor having the tapsMR8, MR8 and MRI and the shunt eld windings of motors MI and M2. Connected across the taps MRS and MR! are the motor eld relay contacts 2FWb and connected across the taps MRS and MRS are the motor eld relay contacts I FWc. Both of these relay contacts are biased to open position and are adapted to be held closed when their corre sponding operating coils 2FW and IFW are energized. Also connected across the busses FBCB-iand FBCB- is a circuit including the brake relay contacts BRd and BRe, both biased to open position but held closed when their operating coil BR is energized; the operating coil of brake I designated as Brake I; and the operating coil of brake 2, designated as Brake 2. A double--pole knife switch KSIS (Fig. 2, pa B) is provided for supplying the operating coils of the contactors and relays from the busses FBCB+ and FBCB-. Said double-pole knife switch KSI9 connects the busses FBCB+ and FBCB- to the wires L3 and L4 respectively.

Connected across the wires Ll and L4 below the knife switch KSIQ is a circuit including the contact X adapted to be operated by a walking beam type push-button, which also contains contacts Y and Z. When the end of the push-button marked Stop-reset is depressed, the contact X is in circuit-closing position and contacts Y and Z are in open position. When the end of the switch marked Run` is depressed, the contacts Y and Z are closed and the contact X is in open circuit position. The letters UV+ indicate a wire whose energization is dependent upon the closure of contacts UVa. When contacts UVa are closed, the wire UV-l is an extension of and has the same polarity as wire L3 and the bus FBCB+. The under-voltage relay contacts UVa are controlled by the operating coil UV. When the coil UV is energized, said contacts UVa are held in closed position, and when said coil UV is deenergized said contacts UVa will be in open position. The circuit which includes the reset contact X also includes the operating coil UV. The contacts UVb, biased to open position, are in shunting relationship with the push-button contact X. Said contacts UVb are held closed when their operating coil UV is energized. Also connected across the wires L3 and L4 below knife switch KSI9 is a circuit including contacts UVc biased to open position; stop button contact Y in closed position; and two branches, as follows: The first branch includes the contact D adapted to be operated by the walking beam type switch LSUB-RSUB, at one end of which is the button LSUB and at the other end of which is the button RSUB. When said button LSUB is depressed,.said contact D is in closing position, and when said button RSUB is depressed said contact D is in open position. The circuit of the contact D also includes limit switch contacts LS1 and LSB; directional relay operating coil LSU; and Stop button contact Z in closed position. The second branch includes the contact E, adapted to be operated by the walking beam type switch LSUB-RSUB. When the button LSUB is depressed, said contact E is in open position, and when button RSUB is depressed said contact E is in closing position. The circuit of contact E also includes limit switch contacts RS'I and RSS; directional relay operating coil RSU; and stop button Z in closed position. The contacts UVc are adapted to be held closed when their operating coil UV is energized. Connected across the wires UV-I and L4 are two branch circuits which include directional contactor operating coils. The irst branch includes the directional relay contacts LSUd and LSUb and directional contactor operating coils LUII, LUI3, LUl and LU23. Said contacts LSUd and LSUb are biased to open position but are held closed when the directional relay operating coil LSU is energized. The second branch includes the directional relay contacts RSUd and RSUb and directional contactor operating coils RUIZ, RUII, RU22 and RUM. Said contacts RSUd and RSUb are biased to open position but are held closed when the directional relay operating coil RSU is energized. Also connected across the wires UV+ and L4 is a circuit composed oi several branches. Common to all these branches are the directional relay contacts RSUc and LSUc (Fig. 2, part C), which are in parallel relationship to each other. The contacts RSUc Aand LSUc are biased to open position, but are held closed when the directional relay operating coils RSU and LSU, respectively, are energized. The first branch includes the contacts 2FTa and ISDRa, in parallel relationship to each other. Timing relay contacts 2 FIa are biased to open position but are held closed when timing relay coll 2FI is energized. First slow-down relay contacts `ISDRa are held open when iirst slowdown relay coil ISDR. is energized. Also included in the first branch is the motor iield weakening relay coil 2F'W and the directional relay contacts RSUc and LSUe, in parallel relationship, both biased to open position. Said contacts RSUe and LSUe are held closed when the directional relay operating coils RSU and ISU, respectively, are energized. The second branch includes motor field weakening relay contacts IFWa, the timing relay operating coil 2FI and, in parallel circuits, directional relay contacts LUIIa, LUI3a, LUIa and LU23a in one of said parallel circuits, and RUI2a, RUIla, RU22a and RU24a in the other of said parallel circuits. Said contacts IFWa are biased to open position and are held closed when motor ileld weakening relay coil IFW is energized. Said contacts LUI Ia, LUI3a, LU2Ia and LU23a are biased to open position, and are held closed when directional contactor operating coils LUI I, LUI3, LU2I and LU23, respectively, are energized. Said contacts RUIZa, RUIIa, RU22a and RUNa are biased to open position and are held closed when directional contactor operating coils RUIZ, RUM, RU22 and RUM, respectively, are energized. The third n branch includes brake relay operating coil BR,

brake relay contacts BRa, biased to open position, generator eld relay contacts GFa, biased to open position, generator field relay contacts GFI a, biased to open position, series brake relay contacts CBRa, biased to open position and in parallel with contacts BRa, GFa and GFIa, and directional contactor contacts LUI Ia, LUI3a, LUZIa and LU23a and RUIZa, RUIla, RU22a and RUZla. Said contacts BRa, GFa, GFIa, CBRa, LUIIa, LUI3a, LUZIa and LU23a and RUIZa, RUIla, RU22a and RU24a are held closed when their respective operating coils BR, GF, GFI, CBR, LUI I, LUI3, LUZI and LU23 or RUI2, RUII, RU22 and RUM are energized. Also included in the third branch is generator ileld relay coil GF, which is in parallel relationship with brake operating coil BR and contacts BRa, GFa and GFI a. Coil GF is also in shunting relationship with contacts IFWa and coil 2F11 in the second branch. The fourth branch includes motor field relay contacts IFWb. biased to closed position; timing relay coil 5T; and generator field relay contacts GFId biased to onen position (Fig. 2, part C). Said contacts IFWb are held open when the operating coil IFW is energized. Said contacts GFId are held closed when the operating coil GFI is energized.

Also connected across the wires UV+ and L4 is a circuit consisting of two branches. Both branches include the directional relay contacts RSUf and LSUf, which are in parallel relationship with each other and which are both biased to open position. The first branch includes first slow-down relay contacts ISDRc, biased to closed position, and timing relay contacts 4Ta, biased is a circuit consisting of three branches.

to open position; field weakening relay coil IFW; and directional relay contacts RSUe and LSUe. which are in parallel relationship to each other and which are both biased to open position. Said contacts ISDRc and 4Ta are in parallel relationship with each other. Said contacts iSDRc are held open when operating coil ISDR is energized, and said contacts 4'la are held closed when operating coil 4T is energized. Said contacts RSUf,

RSUe. LSU! and LSUe are held closed when their respective operating coils RSU and LSU are energized. The second branch includes timing relay coil 4T and generator field relay contacts GFlb, biased to closed position. Said contacts Gmb are held open when operating coil GFI is energized.

Also connected across the wires UV+ and L4 is a circuit which includes generator field operating coil GFI and timing relay contacts ITa, biased to closed position. Said contacts iTa are held open when operating coil iT is energized.

Also connected across the wires UV+ and L4 are two circuits, one of which includes the timing relay coil iT and brake operating relay contacts BRb biased to closed position. Said contacts BRb -are held open when operating coil BR is energized. The other circuit includes timing relay coil 2T and generator field relay contacts GFI b, biased to closed position. Said contacts GFib are held open when operating coil GFI is ener-y sized.

Also connected across the wires UV+ and L4 The first branch includes generator field relay coil GF! and timing relay contacts 2Ta, biased to closed position. Said contacts 2Ta are held open when operating coil 2T is energized. Alternatively, second slow-down relay contacts ZSDRa, biased to open position, may be included in the first branch. Said contacts 2SDRa are held closed when operating coil 2SDR is energized. The second branch includes timing relay coil 3T and generator field relay contacts GFZb, biased to closed position. Said contacts GFZb are held open when operating coil GF2 is energized. Tim- 4o ing relay contacts BTa, biased to open position, connect branches one and two together. Said contacts IIa are held closed when operating coil 8T is energized. The third branch includes timing relay coil 6T and generator eld relay contacts GF3a, biased to open position. Said contacts GFla are held closed when operating coil l GF) is energized.

Also connected across the wire UV+ and L4 is a circuit which includes timing relay contacts .i

lTa. biased to open position, timing relay contacts STa, biased to closed position, generator field relay coil GFS, and directional relay contacts RSUg and LSUc, both biased to open position and in parallel relationship with each other. contacts 5Ta are held closed when operating coil IT is energized, and said contacts 3Ta are held open when operating coil 3T is energized. Alternatively,this circuit may include first slow-down relay contacts iSDRb, biased to open position. Said contacts ISDR are held closed when operating coil ISDR is energized.

Also connected across the wires UV+ and L4 is a circuit which includes the first slow-down relay coil ISDR. directional relay contacts RSUh and LSUh, both biased to open position, limit switch contacts RS! and LSZ. and contact H of a walking beam type push-button. Said contacts RSUh and LSUh are closed when directional relay coils RSU and LSU, respectively, are energized.

Said (,0

The limit switch contacts RSI and LB! are adapted to be controlled by a mechanism to be described presently. Contact H is adapted to be in closed position when the end of the walking beam type push-button marked Normal" is depressed, and in open position when the end of the walking beam type push-button marked Slow" is depressed.

Also connected between the wires UV+ and L4 is a circuit which includes second slow-down relay coil 2SDR, directional relay contacts RSU! and LSUi, both biased to open position, and limit switch contacts RSO and LSI. Said contacts RSUi and LSUj are closed when directional relay coils RSU and LSU, respectively, are energized. The limit switch contacts RSI and IBI are adapted to be controlled by mechanism to be described presently.

The limit switch contacts RSZ, LSI, RSU. IB.. RST, LS1, RSS and L88l are adapted to be bridged and unbridged by bridging members or segments bearing the corresponding reference characters followed by a zero. (Fig. 3.) For example, contacts RSZ are bridged by RS20. The bridging members may be tlxed to a drum, and will move in unison in performing their functions with their corresponding contacts, this movement being responsive to the movement of the skips. The development of the drum segments is illustrated in Figure 3. A cam switch, which is the equivalent, may be substituted for the drum type limit switch I I.

Normal two-motor operation For normal operation the motors MI and M2 for driving the hoist are supplied from generator G2 (Fig. 2, part A). Generator Gi is normally used to supply the D. C. constant potential busses CPB+ and CPB for auxiliary power around the blast furnace area. Both generators are driven by a synchronous motor designated as MJ.

To operate in this manner, double-pole knife switch KST is thrown downwardly to connect r the armature-of generator G2 to the adjustable voltage busses HMB+ and HMB- for the hoist motors. Double-polev knife switch KSi is left open. Double-pole knife switch KS2 is closed upwardly and double-pole circuit breaker BKRI is closed to connect the armature of generator Gi to the constant potential busses CPB+ and CPB-. The double-pole circuit breaker BKRJ is closed and the double-pole circuit breaker BKR2 is left open. Closure of circuit breaker T5 BKR3 connects the ileld windings of motor M3 and the field, brake, and control busses FBCB+ and FBCB- to the constant potential busses CPB-land CPB. Single-pole knife switch KS! is closed upwardly. Double-pole knife switch KSiil is thrown upwardly for self-excitation of generator Gi through its generator field rheostat,

Gen. I fid. rheo. Double-pole knife switch KSII is thrown downwardly to connect the field of generator G2 to the field and brake control busses FBCB+ and FBCB- through resistors R5-R9.

Double-pole knife switch KSIB is closed to connect the field. brake, and control busses FBCB+ and FBCB- to the wires LI and L4.

Assume that the right skip is to be hoisted. The under-voltage relay coil UV (Fig. 2, part B) is connected across the wires LI, L4. Energization of the coil UV is accomplished by depressing the "Stop-Reset button (Fig. 2, part B), thereby moving the contact X into closing position. Energizatiol` of the coil UV results in the closure o! the contacts UVb, which provide a holding circuit for coil UV. Thus contacts UVb remain closed after the Run" button is depressed. moving contact X to open position.

When the holst is at rest, although the motor generator set M3, GI and G2 is in operation, the generated voltage of generator G2 is zero because generator field relay contacts GFb are open. The motor brakes Brake I and Brake 2 (Fig. 2, part B) are set, and motor shunt fields Mtr. I sh. iid. and Mtr. 2 sh. tid. (Fig. 2, part B) are weakened by resistance MRS-MRM).

' To start the movement of the right skip from its lowermost position, thel push-button RSUB (Fig. 2, part B) is depressed, moving the contact Etoits closed position. This results in the energization 'of the coil RSU (Fig. 2, part B), since the limit switch contacts RSI and RS8 are bridged by segments RS10 and RSBII at this time (Fig. 3). The circuit is through UVc; contacts Y; RSUB; contact E; RSS; RSU; RSI; and contact Z to wire L4. Energization of the coil RSU results in the closure of the contacts RSUb and RSUd (Fig. 2, part B), causing the energization of the coils of directional contactors RUI2, RUM, RU22 and RU24 (Fig. 2, part B), which results in the closing of contacts RUIZb, RUNb. RU22b and RU24b (Fig. 2, part, A). This completes the main circuit of the armature of generator G2 (Fig. 2, part A) and the armatures of the hoist motors MI and M2 (Fig. 2, part A) through the hoist motor busses HMB+ and HMB- No current flows in this circuit at this time, however, inasmuch as the generator field circuit marked Gen. iid. 2 (Fig. 2, part B) is open at the contacts GFb. y

Closure of the contacts RSUf (Fig. 2, part C) results in the energization of timing relay 4T (Fig. 2, part C). This causes contacts 4Ta to close. resulting in the energization of field relay coil IFW (Fig. 2, part C) through contacts RSUe (Fig. 2, part C), which had closed previously.

Energization of coil IFW results in closure of contacts IFWc (Fig. 2, part B) which short-circuit the section MR8-MR9 of the resistor in circuit with motor shunt fields Mtr. I sh. iid. and Mtr. 2 sh. iid. of motors MI and M2. Energization of coil IFW also results in the closure of contacts IFWa (Fig. 2, part C), which causes timing relay 2FT to be energized through contacts RSUc, which had closed previously, and through contacts RUIZa, RUIda, RU22a and RU2Ia, also previously closed. This causes closure of contacts 2FIa, which results in energization of field relay coil 2FW (Fig. 2, part C). Energization of coil 2FW4 results in closure of contacts 2FWb (Fig. 2, part B) which shortcircuit the section MRS-MRS of the resistor in circuit with Mtr. I sh. iid. and Mtr. 2 sh. fld. Thus, these motor elds are strengthened and forced to approximate saturation.

The energization of operating coils RU I 2, RU I 4. RU22 and RUN also results in the closure of contactsRUl2a, RUI4a, RU22a and RUZla (Fig. 2, part C), which causes the energization of the generator field relay coil GF (Fig. 2, part C). Energization of this coil results in the closure of contacts GFb (Fig. 2, part B), which completes the circuit of the eld winding Gen. fid. 2. this circuit including the resistor R-R9. Voltage is therefore developed in the armature of generator G2 (Fig. 2, part A), and current flows in the main circuit through the hoist motor busses HMB+ and HMB- and through the 14 armatures o( the hoist motors MI and 2, part A).

Current in this circuit flowing through the brake relay series coil CBR (Fig. 2, part A) resuits in the closure of the contacts CBRa (Fig. 2, part C),.-thereby energizing the brake relay coil BR. Energization o! coil BR results in the closure oi the contacts BRd and BRe (Fig. 2, part B), causing the energization of the coils of Brake I and Brake 2 and resulting in the release of these brakes. The brake coil BR sets up a maintaining circuit for itself through its contacts BRa when relay contacts GFIa close, as later described.

When the brakes release, movement of the hoist starts. The coil of time delay relay IT (Fig. 2, part C) is energized while the hoist is at rest. When brake relay BR closes, the coil oi.' relay I Tis deenergized at contacts BRb. After a predetermined time delay inherent in the relay, contacts ITa close, causing the coil of generator field relay GFI (Fig. 2, part C) to be energized. The result is that contacts GFIc (Fig. 2, part B) close and short-circuit resistance RB-RS in the circuit of Gen. iid. 2, which causes the voltage generated in armature of generator G2 to increase and thereby accelerate the hoist.

Energization of the relay coil GFI causes its contacts GFIb (Fig. 2, part C) to open, thus deenergizing the timing relay coil 2T (Fig. 2. part C). After a predeterminedtime interval inherent in the relay, contacts 2Ta close, and generator field relay coil GF2 is energized, since contacts 2SDRa are closed at this time. This results in closure of contacts GFZa (Fig. 2, part B) and consequent short-circuiting of resistance RB-R'I in the circuit of Gen. fid. 2, which causes the voltage generated in the armature of gener- 40 ator G2 to increase and further accelerate the hoist.

Energization of the relay coil GF2 causes its contacts GF2b to open, thereby deenergizing the time delay relay coil 3T (Fig. 2, part C). After a predetermined time interval inherent in the relay, contacts 3Ta close, and generator field relay coil GF3 (Fig. 2, part C) is energized, since contacts ISDRb and RSUg are closed at this time. This results in closure of contacts GF3d (Fig. 2, part B), which short-circuits resistance RT-RS in the circuit of Gen. fld. 2, and causes a further increase in the voltage generated by the armature of generator G2 to its maximum value.

Energization of generator eld relay coil GF3 causes its contacts GF3b to open, thereby deenergizing the time delay relay 4T (Fig. 2, part C). This results in the opening of contact;y lTa, after a predetermined time interval inherent in the relay, which consequently causes relay coil IFW to be deenergized, since at this time the contacts ISDRc are open. Deenergization of the motor eld relay coil IFW results in the opening of contacts IFWc (Fig. 2, part B), in` troducing resistor MRS-MRS into the eld circuit of motor shunt fields Mtr. I sh. iid. and Mtr. 2 sh. fld. Opening of the contacts IFWa causes time-delay relay coil ZFT (Fig. 2, part C) to be deenergized, thus opening its contacts ZFIa, after a predetermined time interval inherent in the relay, and resulting in the deenergization of motor eld weakening relay coil 2FW, since contacts ISDRa are open at this time. Deenergization of coil 2FW causes contacts ZFWb (Fig. 2. part B) to open, introducing the resistor MRI-MRI into the circuit of motor shunt fields Mtr. I sh. i'ld. and Mtr. 2 sh. iid. The introduction of resistors MRt-MRl-MRI into the ileld circuits of the motors weakens the motor fields and causes the'- hoist speed to increase to its maximum value.

The hoist continues to run at its top speed until the slow-down point is reached as the right skip (the hoisting of which is being discussed) approaches the upper end of its travel. At this point the limit switch contacts R82 (Fig. 2, part C), which-were closed at the beginning oi the cycle, are opened by segment R820 (Fig. 3). 'I'his causes the deenergization oi' the first slowdown relay coil ISDR (Fig. 2, part C) (which had closed when directional relay RSU closed at the beginning ci' the skip trip), resulting in the closure of contacts ISDRc and subsequent energization of the motor iield relay coil IFW (Fig. 2. part C). The energization oi' coil IFW causes contacts IFWc to close and short-circuit the resistor MRI-MRS. Deenergization of coil ISDR also causes contacts ISDRa (Fig. 2, part C) to close, resulting in the energization of motor iield relay coil 2FW. The energization of coil 2FW causes contacts 2FWb (Fig. 2, part B) to close and short-circuit the resistor MRR-MBU. Thus, the motor fields are strengthened and forced.

The deenergization of the ilrst slow-down relay coil ISDR also results in the opening oi its contacts ISDRb (Fig. 2, part C), which are in the circuit of generator field relay coil GFI. 'I'here is no immediate result, since a parallel circuit. through contacts BTa is closed. However, as a n result of the closure of motor field relay IFW, contacts IFWb open (Fig. 2, part C) and the deenergization of time delay relay T follows. In consequence, contacts 5Ta open, after a predetermined time interval inherent in the relay. causing coil GFI to be deenergized. 'Ihis results in opening of contacts GF3d (Fig. 2, part B), which introduces resistor Rl--RB in the circuit of Gen. iid. 2 and causes the voltage generated by the armature of generator G2 to decrease. Consequently the speed of the hoist is decreased.

At the second slow-down point, limit switch contacts RSG (Fig. 2, part C) are opened by segment RS80 (Fig. 3). rlhe second slow-down relay coil 2SDR is thereby deenergized. and contacts 2SDRa (Fig. 2, part C) are opened, resulting in the deenergization of generator ileld relay coil GF2, since contacts BTa normally will have opened by-this time. (Contacts STa open after a time delay after deenergization of coil 8T in response to the opening of contacts GFa.) This causes contacts GF2a (Fig. 2, part B) to open, thus introducing the resistor RB-RI in the circuit of Gen. ild. 2 and causing the voltage generated by the armature of generator G2 to decrease. The result is a further decrease in the speed of the hoist.

The hoist continues to run at this decreased speed until the end of the skip trip. Limit switch contacts RST and RSS (Fig. 2, part B) are then opened by segments R810 and RS80 (Fig. 3), deenergizing the directional relay coil RSU, resulting in the opening of contacts RSUb and RSUd (Fig. 2, part B) and the deenergizing of the directional contactor coils RUI2, RUM, RU22 and RUM. This results in the opening of the contacts RUI2b, RUIlb, RU22b and RUZlb (Fig. 2, part A), thereby opening the main circuit of the motor armatures of the hoist motors MI and M2.

Deenergization of directional relay RSU causes generator field relay coil GF (Fig. 2, part C) to to deenergized. which results in opening of contacts GFb (Fig. 2, part B) in the circuit of Gen. iid. 2 and consequent reduction of the voltage generated by the armature of generator G2 to zero.

Simultaneously, brake relay BR is deenergized, opening its contacts BRd and BRe (Fig. 2, part B), and thereby permitting the brakes Brake I and Brake 2 to set.

Deenergization of directional relay RSU also causes the deenergization of motor field weakening relay coils IFW and 2FW, which results in the openingof contacts IFWc and ZFWb (Fig. 2, part B). Resistors MRG-MRB-MRB are thereby inserted into the circuit of motor shunt fields Mtr. I sh. fld. and Mtr. 2 sh. iid. to decrease the heating of these ileld windings while the hoist 20 is at rest.

The procedure above discussed has brought the right skip to the top of the furnace and the left skip to the skip pit. When the left skip is loaded, the buton LSUB (Fig. 2, part B) is depressed,

85 causing energization of the directional relay coil ISU and the closure of its contacts LSU?) and LSUd (Fig. 2, part B). This results in the energizatlon of the directional contactors LUII, LUI 3, LU2I and LU23, thus closing the contacts $0 LUI lb, LU|3b, LUZ Ib and LU23b (Fig. 2, part A).

The remainder of the cycle is similar to the cycle previously described in connection with the hoisting of the right skip; it being understood, of course, that contacts LS2, LSB, LS1 and LSB in the limit switch govern the circuits in the upward travel of the left skip. since the directional relay coil LSU is energized at this time and the directional relay coil RSU is deenergized at this time.

Normal operation of generator G1 Generator GI is normally operated as a constant-voltage, self-excited shunt generator to furnish general D. C. power in the blast furnace area by means of the constant-potential busses CPB+ and CPB. In the event that generator GI at any one of the blast furnace locations breaks down, this bus may be tied to similar w busses at the other blast furnaces. It is preferable to operate with the double-pole tie circuit breaker BKR! (Fig. 2, part A) open, so that generator GI does not normally operate in parallel with similar machines at the other blast furnaces.

However, it is permissible to operate with these machines in parallel.

. For normal operation single-pole knife switch KSB is closed upwardly; double-pole knife switch KS2 is closed upwardly to connect the armature 6 of generator Gl to the 25o-volt constant potential busses CPB+ and CPB- and double-pole knife switch KSIO is closed upwardly for excitation oi the shunt eld Gen. iid. I of generator GI through the rheostat Gen. I d. rheo. This rheostat Gen. I d. rheo. is adjustable and is set so that the generator GI will deliver the required voltage. Double-pole circuit breaker BKR3 is closed to connect the ileld and brake control busses FBCB+ and FBCB- to the constant potentiaibusses CPB+ and CPB-. Double-pole knife switch KSI is left open. Double-pole circuit breaker BKRI is closed to connect generator GI to the 250volt constant potential busses CPB+ and CPB.

Operation of hoist from generator No.*1

In the event that generator G2, which normally supplies the hoist motors MI and M2 through the hoist motor busses HMB+ and HMB, is out of service, generator =GI may be removed from the busses CPB+ and CPB, which it normally supplies,4V and used to supply the hoist motors MI and M2 through the hoist motor busses HMB-iand HMB-. For this operation, double-pole knife switch KS2 is closed downwardly to connect generator GI to the adjustable voltage hoist motor busses HMB+ and HMB- double-pole knife switches KSI and KSI are left open; double-pole circuit breaker BKR3 is closed to connect field windings Syn. mtr. fid. of motor M3 and field and brake control busses FBCB+ and FBCB- to the 250-volt constant potential supply now obtained through the closed double-pole circuit breaker BKR4 from the tie circuit, Tie circ. Double-pole knife switch KSIU is thrown downwardly to connect the field Gen. fld. I of generator GI to the field and brake control busses FBCB+ and FBCB- through resistors R5-R9. Double-pole knife switch KSI I is left open. Single-pole knife switch KS5 is closed upwardly, double-pole circuit breaker BKRI is left open, and the double-pole circuit breaker BKR3 is closed to energize the field and brake control busses FBCB+ and FBCB- and to provide a supply for the field Syn. mtr. fld. of motor M3. The hoist'will now function, supplied by generator GI.

Operation of hoist when synchronous motor or A. C. supply is not available In the event that the synchronous motor M3 breaks down, or the A. C. supply fails, the hoist may still be kept in operation by running generator GI as a motor to drive generator G2.

The motor-generator set M3, GI and G2 is assembled with a generator at each end and the driving motor between. If it becomes necessary to remove the driving motor for repairs, provision may be made to connect the shafts of generator GI, operating as a motor, and generator G2. For this purpose a dummy shaft may be used in connection with the couplings Coup. I and Coup. 2 (Fig. 1).

For this operation, knife switches should be set as for normal two-motor operation with the following exceptions:

(l) Single-pole, double-throw knife switch KS5 is closed downwardly to include the starting equipment in the armature circuit of generator GI, now to be used as a motor.

(2) Double-pole circuit breaker BKR3 is closed to connect the field and brake control busses FBCB-iand FBCB- to the constant-potential busses CPB-iand CPB-, now supplied through tne double-pole circuit breaker, BKRA, from the tie circuit, Tie circ.

(3) Double-pole knife switch KSI, for starter control is closed.

When knife switch KSI is closed, timing relay coil IAT (Fig. 2, part A) is energized and closes its contacts IATa. The starting operation is now begun by depressing the start button Start, thereby moving the contact P into bridging position. The result is energization of contactor coil IGM (Fig. 2, part A), which provides its own holding circuit by closing of contacts IGMa. Energization of coil IGM also results in closure of contacts IGMd, which completes the main circuit of armature GI, through the resistance 18 A RI-Rl, thus starting the motor at a slow speed. A further result of energization of coil IGM is the opening of normally closed contacts IGMb, which causes timing relay IAT to be deenergized. After a predetermined time interval, contacts IATb close, which results in the energization of accelerating contactor coil IA, as contacts IGMc are closed at this time. Closing of coll IA causes contacts IAb to close the short-circuit resistance Fil-R2, which results in an increase in speed of the motor. Closure of contacts IAb also causes timing relay coll 2AT to be deenergized. Thus, after a time interval, contacts 2ATa close, and accelerating contactor coil 2A is energized, as contacts IAa have closed previously. Energization of coil 2A causes contacts 2Ab to close and short-circuit resistance ft2-R3, which results in the motor being further accelerated. Closure of contacts 2Ab also causes timing relay 3AT to be deenergized. Thus, after a time interval, contacts 3A'I`a close, and accelerating contactor coil 3A is energized, as contacts 2Aa have closed previously. Energization of coil 3A causes contacts 3Aa to close and short-circuit resistance RI-Rl, which results in the motor being accelerated to the speed required for driving generator G2. This speed is determined by the setting of the generator field rheostat Gen. i iid. rheo., which is adjustable.

Operation of generator G2 to supply constantpotential busses In the event that one of the blast furnaces is shut down, provision may be made to supply the constant-potential busses CPB-iand CPB- from both generators operating in parallel, if the extra capacity is needed. For this operation all the knife switches are open except as follows: Double-pole knife switches KSI!) and KSII are thrown upwardly for excitation of the fields of both generators GI and G2 through their respective rheostats Gen. I fid. rheo. and gen. 2 d. rheo. These rheostats are adjustable and are V,set so that the generators will deliver the required voltage and divide the load properly. Doublepole knife switch KS2 is thrown upwardly to connect the armature of generator GI to the constant-potential busses CPB+ and CPB- through double-pole circuit breaker BKRI, which is closed. Single-pole knife switch KSS is closed upwardly and double-pole knife switch KSI is closed upwardly to connect the armature of generator G2 to the constant-potential busses CPB-iand CPB through double-pole circuit breaker BKR2, which is closed. Double-pole circuit breaker BKR3 is closed to energize the field and brake control busses FBCB-iand FBCB- from the constant potential busses CPB+ and CPB-. Thus generator GI provides excitation for the field, Syn. mtr. fid. of motor M3 and the generator fields Gen. iid. I and Gen. iid. 2.

Short description of actual installation An abridged review of the instrumentalities above described will be made by a description of an arrangement which has been installed at a group of three new blast furnaces in which a single three-unit motor generator set is located at each blast furnace.

In the installation referred to, each motor generator set comprises a 600 H. P. synchronous motor driving two approximately duplicate generators corresponding, respectively, to the synchronous motor M3 and the generators Gi and i9 G2 above described. One of these generators is rated at 250 kilowatts, 300 volts. This generator supplies adjustable voltage for the two motors driving the skip hoist, which tw'o motors have been indicated hereinabove by the characters M l and M2. The other generator is rated at 200 kilowatts, 240 volts. A generator rated at 250 kilowatts at 300 volts will have a current rating of l=833.33 ampcres If such a generator is operated at 240 volts, its capacity is In other words, generators G-l and G-Z are of approximately equal capacity. This generator supplies the constant potential direct current service to the scale car, cranes, and other auxiliary drives about the furnace.

The general scheme of connections is illustrated in Figure 1, which shows the arrangement for a plurality of furnace` installations, the showing being in single-line schematic manner. Figure 1 illustrates two blast furnace installations connected by the tie circuit Tie circ. Any number of blast furnace installations may be connected to said tie circuit. Under normal operation generator G2 at each blast furnace will be connected to the corresponding hoist motor busses HMB-iand HMB- and will supply ad- Justable voltage to the hoist motors MI and M2 forming part of that particular blast furnace installation.

As illustrated in Figure 2, part B, and in Figure =200 kilowatts 4, the field windings of this generator are controlled by resistors RS-RS and by relays GFb, GFI c, GF2a and GF3d. Under the normal conditions referred to, the generator Gi will be connected to the constant voltage busses CPB-i and CPB-. Thus generator GI will furnish the excitation for the fields of all the machines. The brakes are also fed from this circuit. A number of feeders are provided to supply auxiliary motors in the local furnace area. The voltage of generator GI is controlled by a hand rheostat.

In the event that a fault should develop in the direct-current generator G2, the transfer switch KS2 may be thrown to connect generator GI to the adjustable voltage hoist motor busses HMB-land HMB-. The generator field transfer switch KSIU is also thrown so that the fields of generator Gl are controlled by resistors R-RS and by the relays GFb, GFIc, GF2a and GF3d. Generator Gl can then serve as a full replacement for generator G2. Two alternative sources of ad- Justable voltage for the hoist motors are thus afforded.

If generator GI should be employed to supply adjustable voltage, it will be necessary to provide some other source of constant-potential directcurrent. This is done by means of the tie circuit, Tie circ., to which the constant-voltage busses CPB-iand CPB- at all of the blast furnace installations may be connected. The tie circuit is extended to a nearby substation which can supplement the direct-current interchanged between the blast furnace installations, if need be.

Thev direct-current unit GI is also provided with a resistor bank and starting contactors, the

combination of said resistor bank and starting contactors being represented by the word Starter in Figures 1 and 4. In Figure 2, part A,

the resistors forming part of this starter are shown as RI-R2-R2-Rl and the contactors (coils) of said starter are shown as IA, 2A, 2A and IGM. The unit GI may then be employed to drive the generator G2. Generator 2 then functions in its normal manner to supply adjustable voltage to the hoist motors Mi and M2. This arrangement protects against the contingency of a fault in the synchronous motor M2, or in the alternating current supply line, or in the switching.

To permit the synchronous motor M2 to be removed for repairs, if need be, a spare section of dummy shaft (not illustrated) may be provided. This dummy shaft replaces the motor M3, being connected to the shafts of the generators Gl, G2, by means of the couplings Coup. i and Coup. 2 (Fig. 1).

Another combination may be described as follows: The two generators Gl and G2 may both be connected to the constant-potential busses CPB-l and CPB-. Such an arrangement is feasible if the blast furnace with which these units are associated is shut down. For example, if the motor M3 at furnace No. i (Fig. 1) is out of service, the generator GI at that furnace may act as a motor to drive the generator G2 which will serve the skip hoist at that furnace. To supply the direct-current to the unit Gl at the furnace No. I, the generators Gi and G2 at blast furnace No. 2 may deliver constant voltage to the tie circuit Tie circ. The combination just described is well adapted to conditions at certain plants. It insures continuity of operation through duplication of facilities without the installation of any idle reserve equipment.

The term skip hoist control as used in this specification is intended to be sufficiently broad to cover the hoist drum means, the motive means for applying mechanical power to said drum means, the motor generator sets, and the control assemblies therefor.

Though a preferred embodiment of the present invention has been described in detail, many modifications will occur to those skilled in the art. It is intended to cover all such modifications that fall within the scope of the appended claims.

What is claimed is:

1. In a skip hoist control, in combination, a driving motor and a pair of direct current generators adapted to be driven by said motor, a skip hoist embodying motive means adapted to be supplied with current from one of said generators, means for adjusting the voltage of said one generator for controlling the speed of said skip hoist, means for providing constant voltage at the terminals of the other of said generators, and means operative alternatively with said first mentioned adjusting means for regulating the voltage of said one generator to provide constant voltage at .its terminals.

2. In combination, a plurality of skip hoists each including motive means and each adapted to operate the skip mechanism at a corresponding location, a plurality of motor generator sets each adapted to supply the motive means at a corresponding one of said skip hoists, each of said motor generator sets comprising a driving motor and a pair of generators of approximately equal capacity adapted to be driven by said motor, a plurality of hoist motor bus means each adapted to be supplied by one of the generators at a corresponding location, means for adjusting the voltage applied by said one generator to its corresponding bus means at each of said locations for adjusting the speed oi' its correspondinghoist, a plurality of constant potential bus means each adapted to be supplied by the other generator at a corresponding location, means for maintaining substantially constant the voltage applied by said other generator to its corresponding bus means at each oi said locations and means forA transferring power at substantially constant voltage from the constant potential bus means at any ot said locations to the other constant potential bus means at any of the other oi.' said locations.

3. In combination, a plurality of skip hoists each including motive means and each adapted to operate the skip mechanism at a corresponding location, a plurality oi motor generator sets each adapted to supply the motive means at a corresponding one of said skip hoists, each of said motor generator sets comprising a driving motor and a pair of generators adapted to be driven by said motor, a plurality of hoist motor bus means each adapted to be supplied by one of the generators at a corresponding location, means for adjusting the voltage applied by said one generator to its corresponding bus means at each of said locations for adjusting the speed of its corresponding hoist, a plurality of constant potential bus means each adapted to be supplied by the other generator at a corresponding location, means for maintaining substantially constant the voltage applied by said other generator to its corresponding bus means at each oi! said locations, and a tie circuit for connecting the constant potential bus means at said plurality of motor generator sets.

4. In combination, a plurality of skip hoists,

each including motive means and each adapted to operate the skip mechanism at a corresponding location, a plurality of motor generator sets each adapted to supply the motive means at a corresponding one of said skip hoists, each of said motor generator sets comprising a driving motor and a pair of generators of approximately equal capacity adapted to be driven by said motor, a plurality of hoist motor bus means each adapted to be supplied by one of the generators at a corresponding hoist, means for adjusting the voltage applied by said one generator to its corresponding bus means at each of said hoists for controlling the speed of its corresponding hoist, constant potential bus means each adapted to be supplied by the other generator at a corresponding hoist, means for maintaining substantially constant the voltage applied by said other generator to its corresponding bus means at each of said hoists, and a tie circuit for connecting the constant potential bus means at said plurality of motor generator sets, one of said generators at each of said hoists being adapted to operate as a motor to drive the other of said generators to supply the power for driving its corresponding hoist.

5. In combination, a plurality of motor generator sets, each including a driving motor and a pair of generators driven by said driving motor, constant `potential bus means at each of said sets adapted to be supplied with constant potential by one of the generators at its corresponding set, a tie circuit for connecting together the constant potential bus means at said sets, the other generator at each of said sets having its own individual control means fo'r adjusting the voltage delivered thereby whereby to control the speed of a motor supplied therefrom, one of the generators at each oi said sets being adapted to be operated as a motor to drive the other generator at its corresponding set.

6. In a skip hoist control. in combination, a motor generator set comprising a driving motor and two generators adapted to be driven by said motor, switching mechanism for alternatively connecting either of said generators to motive means for a skip hoist for driving the skip mechanism of a blast furnace, control means responsive to said skip hoist for adjusting the voltage of one of said generators, switch mechanism for connecting said control means selectively to either ot said generators, and means for maintaining substantially constant voltage on the other of said generators.

7. In a skip hoist control, in combination, a

motor generator set comprising a driving motorA and two generators adapted to be driven by said motor, switching mechanism for alternatively connecting either oi said generators to motive means for a skip hoist for driving the skip mechanism of a blast furnace, control means responsive to said skip hoist for adjusting the voltage of one of said generators, switch mechanism for connecting said control means selectively to either of said generators, and means for maintaining substantially constant voltage on the other of said generators, said driving motor being removable. the rotors of said two generators being adapted to be connected together whereby one of said generators may operate as a motor for driving the other of said generators.

8. In a skip hoist control, in combination, a motor generator set including a driving motor and two generators adapted to be driven by said motor, means for adjusting the voltage developed by one of said generators according to a predetermined plan, means for maintaining a constant voltage from the other of said generators, and switch means adapted to connect either of said generators to said adjusting means whereby either of said generators may ybe controlled by said adjusting means to develop adjustable voltage.

9. In a skip hoist control, in combination, a motor generator set including a driving motor and two generators adapted to be driven by said motor, means for adjusting the voltage developed by one of said generators according to a predetermined plan, means for maintaining a constant voltage at each of said generators, and switch means adapted to connect either or both of said generators alternatively to said voltage adjusting means or to said constant voltage maintaining means whereby either or both of said generators may be controlled to maintain constant voltage.

10. In a skip hoist control, in combination, a motor generator set including a driving motor and two generators adapted to be driven by said motor, means for adjusting the voltage developed by one of said generators according to a predetermined plan, means for maintaining a constant voltage developed by the other of said generators, and switch means whereby one of said generators may be operated as a motor to drive the other of said generators as a generator.

1l. In a skip hoist control, in combination, a motor generator set including a driving motor and two generators adapted to be driven by said mo tor, means for adjusting the voltage developed by one of said generators according to a predetermined plan, switch means adapted to connect said voltage adjusting means to either of said generators, bus means adapted to be supplied by the generator which responds to said voltage adjust-l Y 

